Light sensitive diazotype material



LIGHT SENSITIVE DIAZOTYPE MATERIAL Joseph F. Kosalek, Binghamton, and John Sulich, lin, Endicott, N. Y., assignors to General Aniline & Film Corporation, New York, N. Y., a corporation of Detaware No Drawing. Application February 10, 1954, Serial No. 409,522

9 Claims. (Cl. 95--6) The present invention pertains to light sensitive diazotype materials having fast printing speed and being capable of yielding images of high density, and more particularly to such materials in which the light sensitive component is located on the base in a layer comprising a polyvinyl ester having finely divided alumina dispersed therethrough.

It has become customary with users of the diazotype process and sensitized materials therefor to demand faster printing materials which, at the same time, yield images of higher density upon a clean white background. Inasmuch as the diazotype process in commercial use is a bleach-out, positive process it is manifest that problems are encountered in meeting these demands. If, for example, one uses a given diazo of a certain ultraviolet light sensitivity it is obvious that a reduction in concentration of the diazo will permit one to achieve faster printing speed. This is, of course, attributable to the fact that one need burn out less diazo in order to obtain the image. It is equally evident, however, that the increase in printing speed is only obtained by a sacrifice in the azo dye density of the image produced by development. Meeting the requirements of the art is, therefore, not as simple as it appears.

The difiiculties involved have been recognized and have been grappled with by those in the industry. Several shrewd approaches to a solution have been made, certain of which have achieved great success and others of which have been of little moment. Despite the progress which has been made the art is a long way from providing a product of optimum characteristics.

The most obvious approach to the problem involved is the selection of a diazonium compound having such a high light sensitivity that it may be used in a concentration which will give the required image density while still permitting complete burn-out in the Whites in the desired period of time. To this end, numerous diazos of widely varied chemical structures have been proposed, synthesized and tested in the diazotype process. Of these compounds the stabilized diazos derived from N,N-disubstituted-p-phenylenediamines appear to olfer the best compromise between high light sensitivity and greater dye density, on the one hand, and the other requisite features such as water solubility in coating solutions, stability to decomposition and/of precoupling, fastness properties and the like, on the other hand.

Another tack has been the use of additives in the diazotype coating solution to increase the burn-out sensitivity of the diazo in the light struck areas. For this purpose there have been proposed such compounds as anthraquinone disulfonic acid, ketonic organic compounds and the like. It is evident that this phenomenon, if success ful, would permit more diazo to be used in the sensitized layer and thereby result in a higher density in the ima e areas with no sacrifice in printing speed. Unfortunately,

this approach has met with but limited success, the re- 2,746,863 Patented May 22, 1956 sults not being commercially satisfactory on a quality or cost basis.

A further approach has been to utilize the image surface more efiiciently by the application of a more or less discontinuous layer of a chemically-inert, but physicallyactive, finely divided material such as finely divided silica. In this procedure it has been suggested that such layer be applied by pretreatment of the base or that it be layed down from the coating solution. Thus, U. S. P. 2,433,515 (Reissue 23,510) suggests the formation of a discrete siliceous layer from a colloidal liquid dispersion of silica as a pretreatment for paper, which is then sensitized with a blue print solution. It is claimed that the bright ness and density in the resulting print are thereby enhanced. Conversely, U. S. P. 2,566,709 proposes to produce the same improvement in the diazotype system of photoreproduction by the incorporation of colloidal silica in a dispersed state in a diazotype sensitizing solution. The latter procedure has the very important added economic advantage of eliminating a separate coating step.

It has been found in practice, however, that these two procedures possess certain disadvantages, the gravest of which are (l) rub-ofi; (2) the action of the silica layer as a chromatographic separator, and (3) cost.

Rub-cit, or powdering-olf, as the name implies involves the tendency of the silica particles to be removed during manufacture and end use of the diazotype materials. This action is not only very annoying but in addition may present potential health hazards.

It has been ascertained also that the silica layer acts as a chromatographic separator toward the several ingredients present in a typical diazo coating solution. This results in poorer stability, poorer fade resistance, and, in the case of the black line (which uses a multiplicity of coupling components) off-colored blacks.

It has been stated that the use of the silica layers in the above patents enhanced brightness and density. It is to be noted, however, that the degree of improvement when weighed against the aforesaid objections, the increased cost and extra efforts is disappointingly small.

In U. S. P. 2,662,013, issued December 8, 1953, it is suggested that the above disadvantages be eliminated by the use of binding agents for the silica particles. As such binding agents it is proposed to use those containing chemically bound nitrogen, either in the form of naturally-occurring proteinaceous materials or synthetic resins. It was discovered that the proper ratio, experimentallydetermined, of silica to binder was of critical importance. In fact, it was found that at the proper ratio of silica and binder, a synergistic efiect took place, to wit, density enhancement was out of all proportion to that obtained when either component was used alone or when the two were used together at concentrations other than optimum. Further studies revealed that silica particles of l to 5 micron size gave appreciably greater density enhancement than the smaller particles recommended in the aforesaid patents. However, particles above 10 micron size were avoided since they were difficult to maintain in suspension in the precoating bath and produced undesirable surface roughness in the dried coating.

The procedure of the above patent was a marked commercial advance. However, it had one drawback, this being the incompatibility of the suggested binders with the requisite ingredients of the sensitizing solution. As a consequence, it is necessary in operating according to the above patent to apply the silica-binder dispersion in a separate precoating operation. The use of two coating operations, coupled with the extra handling of the materials involved, manifestly increases the production costs.

We finally discovered that the advantages of the above procedure could be obtained while avoiding the additional coati g .Step by using alumina in lieu of silica and, as the binder for the alumina, a water insoluble polyvinyl ester compatible with the ingredients of the sensitizing solution. Sensitizing solutions containing a polyvinyl ester as the binder, along with finely divided alumina, light sensitive diazotype materials prepared from such compositions, and the processing of such diazotype materials therefor, constitute the purposes and objects of the present invention.

The water insoluble polymers, the use of which is contemplated herein, may be a polyvinyl ester per se, such as polyvinyl acetate, polyvinyl chloride or the like, or copolymers of a vinyl ester, such as vinyl chloride, vinyl acetate or the like with another vinyl compound copolymerizable with such ester, i. e., acrylic acid, styrene or the like. The vinyl ester in such copolymers will range from 10 to 40 parts by weight. These polymers and copolymers are employed in the form of aqueous dispersions in which the solids content is 4055% by weight. Such polymers are readily obtainable in the open market.

Our experiments to date indicate that the polyvinyl esters in such dispersions, in order to be effective, must possess either a cationic charge or must possess no charge, i. e., be non-ionic. If the polyvinyl ester carries an anionic charge it is incompatible with the coupler of the sensitizing solution causing premature precipitation thereof. The use of such polymers must be avoided at all cost. Polyvinyl esters containing a cationic charge produce best results and are, therefore, recommended for use.

The alumina which we use in our dispersions may be either colloidal in character or may be of a coarser grade, i. e., ranging from 1 to 5 microns in size. We find that We obtain best results with the coarser particles and so prefer their use.

Any of the usual light sensitive diazonium compounds may be employed and, in this connection, reference is made to the compounds referred to in U. S. P. 2,501,874, and in the article by Van der Grinten, Photographic Journal, vol. 92B, 1952, page 46. The stabilized diazos derived from N,N-disubstituted p-phenylenediamines are most satisfactory. Examples of such diazos are those derived from N,N-diethyl-p-phcnylenediamine; N-benzyl- N-ethyl-p-phenylenediamine; N-ethyl-p-phenylenediamine; N-phenyl-p-phenylenediamine; N ,N diethyl-Z-ethoxy-pphenylenediamine; N-ethyl-Z-methyl-p-phenylenediamine; N,N bisUi-hydroxyethyl) -p-phenylenediamine N-B-hydroxyethyl-N-methyl-p phenylenediamine and the like. According to customary procedure these diazos are used in the form of salts stabilized with zinc chloride, tin

chloride, cadmium chloride and the like.

The comments with regard to the diazonium compounds apply equally to the coupling components. Thus, any of the usual coupling components are satisfactory for our purpose. Examples of such couplers are 2,5-Xylenol; 2,3-dihydroxynaphthalene; I-S-dihydroxynaphthalene; resorcinol; octyl resorcinol; p-methyl-N-phenyl pyrazolone; the amide of wresorcylic acid; 2-hydroxynaphthalene-3,6- disulfonic acid; H acid; acetyl acetanilide; 2,3-dihydroxynaphthalene-6-sulfonic acid and the like. Other couplers are mentioned in the Van der Grinten article supra.

The coating solution, in addition to the polymer, alumina and light sensitive diazo may contain the various adjuncts usual in the manufacture of light sensitive diazotype materials. These include metal salts for intensification of the dyestuff image, such as ammonium sulfate, nickel sulfate, zinc chloride and the like; stabilizing agents such as thiourea, thiosinamine, naphthalene trisulfonic acid and the like; acids acting to retard precoupling such as acetic acid, boric acid, tartaric acid and the like; hygroscopic agents such as glycol, glycerin and the like; and wetting agents such as saponin, lauryl sulfonate, keryl benzene sulfonate, the oleic acid amide of N-methyl taurine and the like.

It is also recommended that ag be used which the property of accelerating the rate of azo dye color development, particularly under conditions of low ammonia concentration. For this purpose there are used thiourea derivatives and particularly those in which either one or both nitrogen atoms are substituted by an aliphatic radical. Examples of such compounds are 1-allyl-3-18- hydroxyethyl-Z-thiourea; 1-allyl-2-thiourea and the like.

The ratio of alumina to binder is not as critical in our procedure as in the procedure of U. S. P. 2,662,013. Thus, the quantity of binder may range from 1/6 to 1 part by weight for each part by Weight of alumina. The quantity of alumina, on the other hand, based on the Weight of the light sensitive diazonium compound is about 1 part of the diazonium compound to 1 to 4 parts of alumina.

The base to which our coating solution is applied may me any of the bases which have been previously suggested for use in the diazotype field. Examples of such bases are high grade all-sulfite bond paper, rayon or cotton cloth, starch filled cloth, partially hydrolyzed cellulose acetate filmbase, regenerated cellulose acetate and the like.

One of the particular advantages of our development is the fact that it may be used not only with the dry development process, but also with the one component moist process. It is recommended that when the latter procedure is employed, a small amount of a fluoride be added to improve the solubility of the diazo in the coating solution. For this purpose there may be employed ammonium bifluoride, sodium fluoride, potassium fluoride and the like. Generally, these salts are added in an amount ranging from .5 to 4 grams per hundred cc. of coating solution.

Our procedure is carried into effect by dissolving in water the various components of the sensitizing solution and then dispersing therein the desired quantity of alumina and polymer. Any of the apparatus usual for the formation of dispersions may be employed. The base is then coated with the suspension, dried and processed either by the dry or wet method, depending upon whether the coating solution is a two or one component solution.

Our interpretation of the action by which we are able to obtain our results is as follows:

The polyvinyl ester dispersion is essentially composed of discrete water insoluble particles of resin with tiny amounts of polyvinyl alcohol in solution. Being in the insoluble state, the concentration used raises viscosity negligibly compared to what a typical water soluble resin in an equally eifective concentration would. This permits rapid sensitizing and drying during the coating operation. The low pH of the coating solution in combination with the heating applied during the drying step hydrolyzes a small amount of the polyvinyl ester to polyvinyl alcohol on the surface of the particles thus making these particles more receptive to impregnation by the coating solution ingredients. Furthermore, the low block temperature of the resin permits a portion of the particles to fuse during the drying step. This fusion, together with the well-known adhesive qualities of the polyvinyl ester, makes its binding properties upon the silica especially desirable. In the diazotype system in which this polyvinyl ester is used, one can thus visualize the effects of coating solution and resin acting upon one another to produce in a discrete particle, discontinuous film form, a mixture of polyvinyl alcohol and polyvinyl ester, the latter being partially hydrolyzed, unhydrolyzed and partially fused. This mixture represents a very effective manner for receiving the coating solution and enhancing the density of the dye images formed therein.

The invention wili be more fully understood from the following examples which are illustrative only. The parts are by weight unless otherwise stated.

Example I High grade all-sulfite bond paper is coated with a sensitizing solution of the following composition:

and dried. Prints made from these coatings show a considerable enhancement in density when compared to prints made on paper similarly treated with coating solution containing no alumina binder. When compared to prints from coatings made from a solution containing all the above ingredients except the polyvinyl acetate resin, the former had appreciably greater dye density and brightness and showed no tendency for the alumina pigment to rub off, while the latter were markedly inferior in all three respects.

Example II High grade all-sulfite bond paper is coated with a sensitizing solution of the following composition:

and then dried. Prints and comparisons made in a. fashion analogous to those in Example I reveal the same improvements.

Example 111 A high grade, well-sized bond paper is coated with the following solution:

Water 60 Aluminum sulf grams-.. 1.5 Thiourea do 0.5 Citric acid do 0.5 Ammonium hiflunride dn 0,75

4-N-benzyl-N-ethyl benzene diazonium chloride zinc chloride double salt grams Finely divided alumina of 1-5 micron size -do 50% solids cationic type polyvinyl acetate aqueous dispersion or Water to M OBI GD) and then dried. Prints were made and developed in an aqueous solution composed of:

Water cc Sodium carbonate grams 2 Sodium thiosulfate do 5 Thiourea do.. 2.5 Tertiary sodium phosphate do 0.5 Sodium chloride do 4 Phloroglucinol do 1 Resorcinol do 0.5

When these were compared to similarly made prints whose coatings were from a solution not containing the proposed additives, the former were considerably superior in density.

Example IV The procedure is the same as in Example I, excepting that there is employed 50% solids cationic type polyvinyl chloride aqueous suspension in lieu of the polyvinyl acetate of Example I.

Example V The procedure is the same as in Example II, excepting that there is employed, in lieu of the polyvinyl acetate, 50% solids cationic type vinyl acetate-acrylic acid copolymer aqueous dispersion, the content of acrylic acid in said copolymer being 20% by weight.

Various modifications of the invention will occur to persons skilled in the art and we, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A light sensitive composition for diazotype materials comprising a compatible aqueous dispersion of a light sensitive diazonium compound, a coupling component, a water insoluble polyvinyl ester selected from the class consisting of those which are cationic and nonionic and finely divided alumina.

2. The composition as defined in claim 1, wherein the water insoluble polyvinyl ester is polyvinyl acetate.

3. The composition as defined in claim 1, wherein the polyvinyl ester is cationic.

4. The composition as defined in claim 1, wherein the polyvinyl ester is polyvinyl acetate bearing a cationic charge.

5. The composition as defined in claim 1, wherein the alumina has a particle size ranging from 1 to 5 microns.

6. A water receptive base impregnated with a light sensitive composition comprising a compatible aqueous dispersion of a light sensitive diazonium compound, a coupling component, a water insoluble polyvinyl ester selected from the class consisting of those which are cationic and non-ionic and finely divided alumina.

7. The article as defined in claim 6, wherein the polyvinyl ester is polyvinyl acetate.

8. The article as defined in claim 6, wherein the polyvinyl acetate is cationic.

9. The article as defined in claim 6, wherein the alumina has a particle size ranging from 1 to 5 microns.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,991 Neugebauer et al June 25, 1940 2,405,523 Sease et al Aug. 6, 1946 2,522,771 Barnes et al Sept. 15, 1950 

1. A LIGHT SENSITIVE COMPOSITION FOR DIAZOTYPE MATERIALS COMPRISING A COMPATIBLE AQUEOUS DISPERSION OF A LIGHT SENSITIVE DIAZONIUM COMPOUND, A COUPLING COMPONENT, A WATER INSOLUBLE POLYVINYL ESTER SELECTED FROM THE CLASS CONSISTING OF THOSE WHICH ARE CATIONIC AND NONIONIC AND FINELY DIVIDED ALUMINA. 